As was said earlier, talking about oil is like talking about religion - everyone has their own opinion and "sources" to support it.
That being said, glad to hear the Castrol is working good for you too; I'm having the same experience - no complaints using dealer installed Castrol.
I use Amsoil in my diesel truck and tractor and have no complaints there either.
I just can't imagine why a motorcycle company would risk their reputation and financial success by recommending a clearly inferior product. Yep, I understand sponsorships and "money changing hands", but that can't possible compare to the profit from increasing market share and selling more bikes without unnecessary claims.
I think it just reinforces the fact that most high quality
oils with the same technical specs are comparable with little difference in performance IF changed regularly. Therefore there is room for different manufacturers to associate themselves with different brands for "marketing" reasons since performance doesn't really vary that much.
Just an opinion of course - isn't all of this?!